Accident data analysis and on-field inspections. Do they lead to similar conclusions?

Network Safety Ranking and Road Assessment Programme (RAP) are two procedures used in road infrastructure safety management to rank the road sections of a network according to estimated road safety performance. The former uses indicators based on road accidents and their consequences while the latter method is based primarily on inspections of the road infrastructure. The aim of this study was to verify whether there is a relationship between the indicators used within these methods, in order to evaluate if and under which conditions RAP scores contribute to the prediction of accident numbers. The adopted approach is based on the calibration and analysis of a wide array of models in order to reproduce the observed events-injury road accidents, fatalities and injuries-with reference to different aggregations of the original data and in the two reference situations: with and without EuroRAP (European Road Assessment Programme) indicators. From the obtained results, the introduction of the EuroRAP indicators ends up making the models that explain the frequency of accidents more convincing from a statistical point of view. These indicators, which summarise the road safety performance of a road section, could prove useful in replacing the covariates (e.g. presence of intersections, geometrical and functional features of roads) that are used in the calibration of accident prediction models. However, it should be stressed that not all types of accident are addressed by the EuroRAP approach, and this may represent a limitation for those roadways where such kind of accidents are frequently observed, like rear-end collisions on motorways. Probably, by including these accident types, the explanatory power of the EuroRAP variables would increase, at least on motorways.